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While it's no secret that a woman's fertility declines with age, your sperm isn't immune to the aging process either. In fact, research suggests that kids born to men 40 and older have a greater risk of autism and schizophrenia than those younger than 30, and miscarriage rates—as well as certain birth defects such as dwarfism—also rise for women who conceived with older men, according to Roger W. Harms, MD, of the Mayo Clinic.

The reason your swimmers lose some of their power is because the odds of errors in genetic coding increase as we age, researchers speculate. Think about it: After you ejaculate your body has to produce millions of new sperm cells again, and an increase in genetic mutations is a natural part of the aging process.The good news is that simple diet changes can help keep your swimmers healthier for longer. For super sperm, fill up on these nutrients.

Folate

Men low on folate may have 20 percent more unhealthy sperm (swimmers that have missing or extra chromosomes) than those with higher levels, suggests a study in the journal Human Reproduction. If you’d rather not have mutant sperm, try filling up this B vitamin that’s key for cell production.

Which foods pack the most punch: Leafy greens (think: spinach and kale), citrus fruits, and beans are all full of folate. Another source? Avocados, which—not so coincidentally—the ancient Aztecs referred to as “testicle trees.” The recommended daily amount is 400 micrograms, but study authors think upping your intake to 700 micrograms might give sperm extra protection from mutations.

Easy fixes: Swap lettuce for spinach the next time you order a sub, opt for chili with extra beans, or add orange juice to your post-workout smoothie.

Zinc

This mineral is also important for cell division, and thus sperm production. Bonus: Zinc may work as a libido-enhancer by helping with testosterone production, since higher levels of the hormone are linked to an increase in desire.

Which foods pack the most punch: Oysters take the prize, hands down. Besides being known as an aphrodisiac (thanks to their resemblance to a certain female body part), oysters hold more zinc than almost any other food. Aim to eat up to 15 mg daily—about the amount in six oysters. Other good sources include red meat, peanuts, cashews, and pumpkin seeds.